1. Field of the Invention
The present invention relates to railroad switch devices, and more particularly to a switch point position indicator.
2. Description of the Prior Art
Railway turnouts alternately divert trains from one track to another set of tracks. A common turnout used in the industry has a switch property which includes switch points, a switch machine and an operating rod to initiate diversion of the wheels, a frog to carry the train wheel flanges across opposing rails and lead rails between the frog and the switch. The switch points are typically moved by means of the operating rod which is attached to the switch point and is also connected to the switch machine. In operation, the operating rod is translated by the switch machine causing the switch points to move.
Devices for determining whether or not a railroad switch is in the proper position are well known and have been used in switch mechanisms on railroads for many years. A switch circuit controller is a device that is typically mounted to the railroad ties and is connected to the point detector rod. The switch circuit controller provides a signal indicating the position of the switch point. The signal produced by the switch controller is a vital indication which means that the signal need not be checked further and may be presumed to be accurate. A description of typical railway switch circuit controllers can be found in U.S. Pat. No. 5,598,992 to Chew, which patent is assigned to the present assignee and is hereby incorporated by reference herein. By way of brief description, the location of the railroad switch is generally given by determining the location of the connecting rods which connect the switch lever to the railroad switch itself. Thus, the location of the lever is an indirect indication of the actual position of the railroad switch itself.
The railroad industry is a very harsh environment for any product. The environmental conditions that field mounted devices must endure are extremely harsh and design of such components must be very robust to survive. A switching device must enable the mounting and adjustment of the switch point indicators directly to the stock rail while performing dependable sensing of the switch point under all conditions.
The use of proximity sensors mounted to the switch points has previously been proposed. However, this scheme has several disadvantages. Since the railroad switch is exposed to the elements, it is necessary in colder climates to employ switch heaters to melt any snow or ice which could otherwise accumulate on the rails and prevent proper operation of the switch. Thus, mounting the detectors on the switch rails not only exposes these delicate instruments to the heating elements, but also to the hot air directed at the switch. Although the heaters are generally employed, a power interpretation to the heaters would adversely affect the operation of the proximity detectors. Additionally, mounting the sensors to the switch points means that they are also subjected to wear and tear caused by the cycling between the normal and reverse the positions of the switch.
Because of the potential for inaccurate readings due to these adverse operating conditions, a complex controller is typically required to ensure proper sensor operation. For example, in a system having proximity sensors located on the switch rails, as discussed above, Programmable Logic Controllers (PLC) are used in a checked redundant configuration for the switch points. By way of explanation, two proximity detectors are used for switch point detection and each proximity detector is operatively coupled with a PLC.
It is therefore an object of the present invention to provide a fail-safe switch position indication mechanism which more accurately indicates the actual railroad switch position.
It is another object of the present invention to provide a switch point position indicating mechanism which can survive and be dependable in the harsh environment typically found in railroad systems.